1. Field of the Invention
The present invention relates generally to the field of semiconductor manufacturing processes, and more particularly to a method of correcting overlay error in photolithographic processes.
2. Description of the Prior Art
Photolithography is an essential step in semiconductor manufacturing processes, through which the pattern of integrated circuits may be transferred from photomasks to semiconductor chips. Generally, a design layout of integrated circuit provided by an IC design house may be divided into several layers of design layouts after it is received by the semiconductor manufacturing company. These design layouts may be then fabricated on the corresponding transparent plates to thereby form photomasks with desired layouts. The layout of each of the photomasks may be respectively transferred to a photoresist layer on the chip through suitable photolithographic process. Afterwards, other suitable processes, such as etching, deposition, doping and so forth may be carried out in order to obtain required semiconductor devices.
Recently, the measurement of the overlay between two or more successive layers becomes more and more important along with the continuous miniaturization in integrated circuits. For instance, through vias and contacts are often used to electrically connect interconnections in different layers to one another. Because the interconnections, the through vias and/or the contacts are generally disposed indifferent layers, a process of overlay measurement needs to be carried out during each of the corresponding photolithographic processes so as to assure the minimum shift between successive layers.
However, the current overlay measurement still has some drawbacks. For example, due to measurement deviation, the measured values of relative positions between successive layers often fail to reflect their real positions. Therefore, the measurement results often include overlay error.
Accordingly, there is a need to provide an improved method of correcting overlay error so as to increase the accuracy of the measurement results.